The present invention relates to a storage apparatus for magnetically recording and reproducing information to/from a disk medium and, more particularly, to a storage apparatus for reducing a read error caused by a thermal asperity of an MR head.
In association with an increase in information amount in an information-oriented society dealing with multimedia data in recent years, an increase in storage capacity of a magnetic disk apparatus as a peripheral apparatus of a computer is requested. In order to increase the storage capacity, it is necessary to increase a density on a medium recording surface by improving a bit density BPI or a track density TPI per unit length. In order to increase the bit density BPI on the medium recording surface, it is necessary to improve frequency characteristics of a magnetic head or medium, and to improve a magnetic head or a medium such that an output of the head is not dropped even at a high frequency and high frequency noises are not increased.
At present, the magnetic head is divided into a reproducing head and a recording head in order to efficiently reproduce data written in a medium. An MR (Magneto-Resistive) head is used as a reproducing head. The MR head converts a recorded magnetic field change into a resistance value change. The resistance value change is further converted into a voltage change by a preamplifier provided for a head IC, thereby reproducing recording data. When the MR head is used, a thermal asperity (called "TA" hereinbelow) phenomenon becomes a problem. The TA phenomenon is a phenomenon such that a resistance value is rapidly changed by heat generated when an MR device comes into contact with a medium scratch or dust on the medium and a base line of a reproduction waveform is shifted, so that data cannot be reproduced. Especially, since a head floating amount tends to be decreased more and more in order to efficiently reproduce data, there is a tendency such that the TA phenomenon often occurs due to a reduction in medium clearance of the MR head.
In a conventional magnetic disk apparatus, when a read error of data or a read error of servo information occurs by external noises, a shock, or the like, the error is recovered by re-reading the data. That is, the external noises and shock are temporary phenomena and the error can be usually avoided by the re-reading operation. On the contrary, the error due to the TA phenomenon is a fixed error that is caused by a scratch of the medium or the like, so that the error cannot be avoided by the re-reading operation. Usually, the error is regarded as a medium defect and an alternating process is executed. In the conventional magnetic disk apparatus, however, whether the read error is caused by the external noises or the TA phenomenon cannot be distinguished, the re-reading operation is executed in spite of a fact that the error is the unrecoverable error caused by the TA phenomenon. The number of times of the re-reading operations is generally determined to be, for example, 100 times. Consequently, with respect to the read error caused by the TA phenomenon, only after the re-reading operation was performed 100 times, the error is decided to be the unrecoverable read error and a message indicating that the operation was finished as an abnormality is reported to an upper apparatus. Consequently, it takes a long time for a process when the read error occurs due to the TA phenomenon and there is a problem such that an accessing performance of the magnetic disk apparatus largely deteriorates.